The Neural Control of Visually Guided Eye Movements
D. Temporal Factors in Visually Guided Saccadic Eye Movements
          1. The conditions under which express saccades can and cannot be generated.

e. Does the probability with which a target appears at various familiar locations in the scene affect the frequency with which express saccades are generated?

Figure 34 shows data obtained under conditions in which targets at some locations appeared more frequently than at others. Four locations were used, at two of which the single target presented appeared frequently and at two infrequently. In successive sets the position of frequent and infrequent locations was reversed. When the probability of appearance of the target at a given set of locations was high (89%), many express saccades were made to them; when the probability of appearance was low (11%) few express saccades were made. Thus the probability with which targets appear at various locations in space in any given set significantly affects the frequency with which express saccades are generated. This suggests that there is a generalized set of expectations involved in express saccade generation.